The present invention relates to a rotor of a steam turbine of which main steam temperature is 675° C. or more, and to a steam turbine plant.
For improving power generating efficiency of a steam turbine power generation plant, it is effective to increase its main steam temperature. At present, a steam turbine plant of which main steam temperature is more than 600° C. is commercially operated, and a steam turbine of which main steam temperature is of the 650° C. class is under development. Moreover, in order to further improve the efficiency, a steam turbine of which main steam temperature is 675° C. or more, and particularly 700° C. or more is also under development. In the steam turbine aiming at the main steam temperature of 700° C. or more, a conventional rotor material made of steel is not suitable since its allowable temperature is approximately 650° C., and thus, it is necessary to produce the rotor from Ni-base alloy. The Ni-base alloy has higher strength in comparison with the steel material, however, the Ni-base alloy is expensive, and moreover, it is difficult to make a large forged product from the Ni-base alloy. As an alloy from which the large forged product is relatively easily produced, there are raised an A286-type alloy, an IN706-type alloy, an IN718-type alloy and the like. These alloys have been adopted in a gas turbine disk and a power generator rotor for example, as shown in JP-A-10-226837 (the claims) and a non-patent document of CAMP-ISIJ VOL. 15 (2002)-535 (preamble).